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University of Canterbury

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Doctoral

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The New Zealand Building Code Approved Documents have recently incorporated reductions
in the life safety F-ratings, which determine the fire resistance rating (FRR) requirements of fire
barriers in buildings. This reduction has led to concern that in the event of a real fire exposure,
where modern synthetic materials increase both the speed of fire growth, peak heat release rates
and temperatures within a compartment, fires more severe than the AS1530.4 standard furnace
test exposure may result. In such cases construction elements may not provide suitable fire
protection for the life safety requirements of the Building Code. These requirements include
provision for safe evacuation of occupants and fire service rescue activities.
Three full-scale compartment tests were carried out, establishing the actual times to failure of
numerous light timber framed (LTF) and light steel framed (LSF) non-loadbearing wall and LTF
ceiling/floor assemblies. Each test assembly selected had detailed temperature data available
from its respective standard furnace test, which had previously been undertaken to determine
the assemblies FRRs. The compartment assemblies, of ISO 9705 room geometry, were exposed
to fires of varying severity based on the fuel load energy density within the compartment and the
ventilation opening dimensions. Synthetic materials were selected to replicate the initial fast fire
growth associated with upholstered furniture. Wooden cribs were used to provide bulk fuel for
the remainder of the FLED requirement.
A method of predicting assembly failure times when exposed to real fire exposures has been
established. The method is based on a correlation of the cumulative radiant heat energy that
would impact on an assembly up to the point of its failure during a standard test, and the
equivalent time at which a real fire exposure would have produced the same level of cumulative
energy. The method provides good agreement and reasonably conservative prediction of a nonloadbearing
assembly’s insulation failure. Further validation is required to establish factors of
safety to the method for determining assembly integrity failure. The method was found to be
non-conservative for use on loadbearing assemblies.